This invention relates to a machine and process for heat setting yarn, principally, but not exclusively, carpet yarn. The machine conditions twisted yarns with saturated steam to increase the crystallinity of the yarn and lock the twist or the crimp into the yarn. The machine is a continuous process machine with yarn entering one end of the machine, moving downstream through the machine and exiting the downstream end properly treated and ready for the next production step—typically winding onto yarn packages in preparation for carpet tufting.
In general, the heat setting machine includes a coiler or other yarn-depositing device for depositing yarn on a moving conveyor which carries the yarn into a pretreatment chamber where the yarn is heated. The yarn then passes through a set of entrance sealing rolls which maintain a pressurized environment within the system. The yarn then passes into an entrance-cooling chamber where cool, dry air is circulated through the yarn, cooling the yarn to a uniform temperature and thus allowing redevelopment of the bulk in the yarn. This cooling chamber also protects the sealing rolls from the higher temperature of the heating chamber.
The yarn then passes into a heating chamber where a homogeneous mixture of steam and air is circulated through the yarn. The yarn exits the heating chamber into an exit-cooling chamber where cool dry air is circulated through the yarn to reduce the yarn temperature, remove excess moisture, and protect a set of exit sealing rolls which cooperate with the entrance sealing rolls to maintain a pressurized environment within the system. The yarn then passes through the exit sealing rolls and can be further dried, separated and wound onto packages on a take-up winder which runs in synchronization with the remaining components. A yarn accumulator can be part of the system, allowing the system to continue operating during winder doffing cycles.
Several features are provided which differentiate the machine and method disclosed in this application from prior art machines. These features include a tunnel wherein two cooling chambers on either end of a heating chamber communicate in alignment with each other along an axis extending the length of the combined cooling and heating chambers. There is no offset from one zone to the other. This permits less expensive manufacturing and a wider conveyor belt for transporting the yarn through the system.
The novel system also includes an entrance and exit set of sealing rollers which maintain the pressure in the system. These sets of rollers are moved into and out of sealing position by a novel power-assist assembly such as pneumatic or hydraulic cylinders. The rollers are locked into sealing with each other by a mechanical locking device that takes the load off of the power-assist assembly and places the load onto heavy springs which provide the resilience necessary to perform the sealing function while permitting the yarn to pass between the rollers into and out of the heating chamber.
The invention can also include an exterior heat exchanger.